查询

1简单查询

mysql> SELECT CITY,TARGET,SALES FROM OFFICES WHERE REGION='Eastern';

ORACLE和DB2遇到NULL值时什么也不显示

2计算查询

mysql> SELECT CITY,REGION,(SALES-TARGET) FROM OFFICES;
mysql> SELECT NAME,MONTH(HIRE_DATE),YEAR(HIRE_DATE) FROM SALESREPS;
mysql> SELECT CITY,'HAS SALES OF ',SALES FROM OFFICES;

SQL常量可以被其自身用做选择列表的项
-------------+---------------+-----------+
| CITY        | HAS SALES OF  | SALES     |
+-------------+---------------+-----------+
| Denver      | HAS SALES OF  | 186042.00 |
| New York    | HAS SALES OF  | 692637.00 |
| Chicage     | HAS SALES OF  | 735042.00 |
| Atlanta     | HAS SALES OF  | 367911.00 |
| Los Angeles | HAS SALES OF  | 835915.00 |
+-------------+---------------+-----------+15UNION和排序

3选择所有的字段

SELECT ×

4重复的记录

mysql> SELECT DISTINCT MGR FROM OFFICES;

5选择记录

mysql> SELECT NAME,SALES FROM SALESREPS WHERE MANAGER=104;
mysql> SELECT NAME,SALES,QUOTA FROM SALESREPS WHERE EMPL_NUM=105;
mysql> SELECT CITY,SALES,TARGET FROM OFFICES WHERE SALES>TARGET;

6比较测试

mysql> SELECT NAME FROM SALESREPS WHERE HIRE_DATE<'2006-01-01';
mysql> SELECT CITY,MGR FROM OFFICES WHERE MGR<>108;
mysql> SELECT CITY,MGR FROM OFFICES WHERE MGR!=108;

其中<>也可以写作！=。

7范围测试

mysql> SELECT ORDER_NUM,ORDER_DATE,PRODUCT,AMOUNT FROM ORDERS WHERE ORDER_DATE BETWEEN '2007-10-01'AND '2007-12-31';

范围测试包括范围的端点。包括10月1日和12月31日。
A BETWEEN B AND C=（A>=B)AND(A<=C)。否定形式NOT BETWEEN。

8组成员测试

mysql> SELECT NAME,QUOTA,SALES FROM SALESREPS WHERE REP_OFFICE IN(11,13,22);

9模式匹配测试

百分号%通配符字符匹配任何顺序的0个或多个字符。

mysql> SELECT COMPANY,CREDIT_LIMIT FROM CUSTOMERS WHERE COMPANY like 'Smith% Corp.';

下划线_通配符字符匹配任何单个字符

mysql> SELECT COMPANY,CREDIT_LIMIT FROM CUSTOMERS WHERE COMPANY LIKE 'Smiths_n Corp.';

like测试必须应用到具有字符串数据类型的字段
转意字符

mysql> SELECT ORDER_NUM,PRODUCT FROM ORDERS WHERE PRODUCT LIKE 'A$%BC%' ESCAPE '$';

以上是用$来做转意字符的，也可以用不同的字符来做转意字符。

10NULL值测试

mysql> SELECT NAME FROM SALESREPS WHERE REP_OFFICE IS NOT NULL;

这里不能用REP_OFFICE=NULL;因为NULL不是一个真正的值而是一个符号，表示值是未知的，所以不能用=来匹配。

11复合搜索条件

mysql> SELECT NAME,QUOTA,SALES FROM SALESREPS WHERE SALES<QUOTA AND SALES<300000;
mysql> SELECT NAME,QUOTA,SALES FROM SALESREPS WHERE SALES<QUOTA AND NOT SALES<15000;

12排序查询结果

默认情况下排序为升序ASC，降序位DESC。

mysql> SELECT CITY,REGION,(SALES-TARGET) FROM OFFICES ORDER BY REGION ASC,3 DESC;

（不建议）
这里的3也可以用（SALES-TARGET）代替。

13组合查询结果

列出产品价格超过2000美元或在一个订单中订购了超过30000美元产品的所有产品。

mysql> SELECT MFR_ID,PRODUCT_ID FROM PRODUCTS WHERE PRICE>2000.00 UNION SELECT DISTINCT MFR,PRODUCT FROM ORDERS WHERE AMOUNT>30000.00;

注意三点：1,两个SELECT子句必须包含同样数目的字段
    2,第一个表中的数据类型必须与第二个表中对应字段的数据类型相同
    3,两个表都不能用ORDER BY子句排序，但组合后的查询结果可以排序。

14UNION和重复记录

UNION 默认是消除重复的，UNION ALL保留重复记录。

mysql> SELECT MFR_ID,PRODUCT_ID FROM PRODUCTS WHERE PRICE>2000.00 UNION ALL SELECT DISTINCT MFR,PRODUCT FROM ORDERS WHERE AMOUNT>30000.00;

15UNION和排序

mysql> SELECT MFR_ID,PRODUCT_ID FROM PRODUCTS WHERE PRICE>2000.00 UNION SELECT DISTINCT MFR,PRODUCT FROM ORDERS WHERE AMOUNT>30000.00 ORDER BY 1,2;